Asus recommends at least 650W, so 700W should be enough. But of course it always depends on what else is installed.
https://www.asus.com/ch-de/motherboards-components/graphics-cards/tuf-gaming/tuf-rtx3060-o12g-v2-gaming/techspec/
Hello
Please excuse my perhaps weak French (I had to use the Google translator).
To answer your question briefly: Unfortunately, the required cable is not available individually as a spare part.
The required cable (with the red plugs) should normally be attached to the power supply unit according to the 4x instructions.
However, if you do not have these cables, you must order a complete set of cables (not available from Digitec).
Alternatively, you can order individually sleeved cable sets from other portals.
For example this Individually Sleeved Cable Kit - Blue (AC-032-CN5NAN-PB) => https://www.thermaltake.com/individually-sleeved-cable-kit-blue.html
As this kit costs about 80 € (e.g. on Amazon), a new power supply may make more sense for about CHF 140.
Examples Thermaltake:
-> Thermaltake Smart Pro RGB for 133.- (what you mentioned, only designed for 80 Plus Bronze efficiency! 850W) => Thermaltake Smart Pro RGB (850 W)
-> Thermaltake ToughPower GF1 for 147 (designed for 80 Plus Gold! 850W efficiency) => Thermaltake ToughPower GF1 (850W)
What I use now:
-> Corsair CX750F RGB for 141.- ( 80 Plus Bronze efficiency, 750W) => Corsair CX750F RGB (750 W)
I hope I can be of some help.
Sincerely